Fungal diseases of persimmon in semi-arid areas: adaptive strategies and future risks
In east-central Spain, the persimmon-growing area has increased considerably as a result of the popularization of the cultivar 'Rojo Brillante' and the implementation of the postharvest deastringency treatment, which has opened new export markets. Circular leaf spot disease, caused by Mycosphaerella nawae, was first described in Japan and is prevalent in Korea. Both areas have a humid subtropical-type climate, with a summer-rainfall pattern and high annual precipitation. In contrast, the climate in the Mediterranean Basin is characterised by dry summers and low annual precipitation, so persimmons can only be grown with irrigation. Epidemiological studies of circular leaf spot in Spain indicated that all infections were caused by ascospores formed in the leaf litter. Ascospores were released mainly in April and May, much earlier than in Korea, and relatively low numbers in June were able to induce severe symptoms on trap plants. Most infections coincided with rains, but the disease was observed also on trap plants exposed to less than 1 mm of precipitation and even in the absence of rain. These results revealed that M. nawae managed to adapt to semi-arid conditions mainly by changing the period of inoculum production to coincide with rains and susceptible host availability. Postharvest black spot of persimmon, caused by Alternaria alternata, is also responsible of serious yield losses in the Mediterranean Basin. Studies conducted in Spain indicated that the different inoculum sources were broadly distributed in affected orchards and A. alternata conidia were highly tolerant to dry periods. Consequently, airborne inoculum was available throughout the growing season. Latent infections in persimmon fruit were more frequent during the three-month period prior to harvest. Finally, the risk of introduction of exotic fungal diseases of persimmon in semi-arid areas is discussed considering the unforeseen epidemic of circular leaf spot in Spain, which highlights the limitations of climate suitability analyses, especially when based only on limited disease distribution records.
Vicent, A., Mira, J.L. and Bassimba, D.D.M. (2018). Fungal diseases of persimmon in semi-arid areas: adaptive strategies and future risks. Acta Hortic. 1195, 127-132
persimmon, fungal pathogens, epidemiology, risk assessment